Convert Admin "Users" view from HAML to Vue
### Problem to solve
Currently the Admin "Users" view is built with HAML. It should be converted to Vue to support:
- [Displaying user group count](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/44069#note_426348156)
- [Making columns sortable](https://gitlab.com/gitlab-org/gitlab/-/issues/238181)
- [Adding filter categories](https://gitlab.com/gitlab-org/gitlab/-/issues/238183)
### Proposal
The Admin "Users" view should be converted to Vue.
### MVP Implementation
Convert the admin users table to Vue. https://gitlab.com/groups/gitlab-org/-/epics/4961
This is the minimum implementation we need to deliver the issues listed above.
### What's next after we converted the table to Vue?
- Add the missing fields to our REST / GraphQL API
- Create admin users store
- Migrate the admin actions to the store
- edit
- block
- deactivate
- delete
- delete-with-contributions
- Use the URL filter params to fetch the data from the API
See the full implementation with next-ups discussed in https://gitlab.com/groups/gitlab-org/-/epics/4683#note_435131368.
### Related links
- @peterhegman [explained](https://gitlab.com/gitlab-org/gitlab/-/issues/249589#note_426451311) this conversion to Vue would be helpful for 2 gitlab~10046105 features (both mentioned above).
epic